Study on durability testing of concrete under the condition of sulfate

Transcription

1 Acta Technica 62 (2017), No. 6A, c 2017 Institute of Thermomechanics CAS, v.v.i. Study on durability testing of concrete under the condition of sulfate Shen Lin 2, Wang Shaopeng 2, Zhao Shangchuan 2, 3, Li Wanheng 2 Abstract. According to the material degradation of concrete under the condition of sulfate, analysis of concrete durability testing is made. The concept of small-invasive detection based on the rebound method and core drilling method for sulfate attack is proposed. Through the alternation test of wetting and drying on concrete members, the evaluation of durability on sulfate attack is given, which can be used as a reference when detecting and estimating the durability of concrete structures. Key words. Bridge engineering, concrete, durability, sulfate. 1. Introduction It is well-known that the deterioration of durability on concrete under the condition of sulfate is contributed by chemical reaction between hydration products of concrete and sulfate ion, which leading to the loose in texture and decreased in strength of concrete. It can cause the deteriorated of concrete through the longterm association with sulfate environment. XUE Peng-fei formulated a multi-factor diffusion model of chloride in concrete based on the modified hypothesis of Fick s rule [1]. In severe cases, it will directly threaten the operation service period of bridge. Therefore, how to accurately obtain the detection index under the condition of sulfate becomes the key to establish the method of structural durability assessment [2, 3]. At present, there are few researches on the material degradation of concrete under the condition of sulfate. Most experts focus on the changing regularity of parameters, such as strength, relative dynamic modulus of elasticity and mass loss in 1 Acknowledgment - This work is financially supported by the Special Basic Foundation for Central Public Research Institutes ( ) and Construction Technology Projects Motivated by Ministry of Communication ( ). 2 Research Institute of Highway Ministry of Transport, Beijing, China 3 Corresponding Author, shenlin16118@163.com

2 192 SHEN LIN, WANG SHAOPENG, ZHAO SHANGCHUAN, LI WANHENG the laboratory [4]. In particular, the rebound method is suitable for site tests, which need a certain pressure to meet the need of small specimens. However, it will cause some concomitant injury. The compression strength based on ultrasonic method always combined with the rebound method, otherwise, the accuracy of strength could be affected by the humidity, aspect ratio and the location of steel in the concrete. This makes the scope of application of testing curve are limited, and the pull-out method can only be used to test the strength of structures, which can not evaluate the durability of concrete structures under the condition of sulfate. The core drilling method directly drills the samples taken from concrete members for destructive testing. However, it has caused a certain extent of damage to the structural. Based on these reason, the method of durability evaluation on sulfate attack of concrete is given by synthetic analysis. 2. Advantage of hardness testing under the condition of sulfate The hardness testing takes fewer specimens to meet the requirements of alternation test of wetting and drying on concrete, and it gets more data for durability analysis and more accurate in evaluating the durability. Compared with the resiliometer, the durometer is only about 0.5% in impact energy and the ball diameter is much smaller, for details see attached Tables 1. Table 1. Hardness tester and the resilience of the indicators of contrast Competency Indicators M225 Resiliometer TIME5302 Durometer Impact Energy 2.207J 0.011J Ball Head Diameter 25mm 3mm 3. Experiment scheme of durability inspection 3.1. mix proportion design of concrete strength grade water-cement ratio Table 2. Mix proportion design of concrete water kg/m3 cement (kg/m3) sand (kg/m3) stone (kg/m3) water-reducing agent (kg/m3) C C C The mix proportion design of concrete depends on the Specification for Mix Proportion Design of Ordinary Concrete (JGJ ) in the test [5]. The grade of strength for the concrete is ranged from C30 to C50, and water cement ratio are

3 STUDY ON DURABILITY TESTING OF CONCRETE UNDER THE CONDITION , 0.40 and For the concrete pump used in practical project, it is required that the slump of concrete should be maintained in the range of 15-20cm. According to the result of laboratory test, the dosage of water-reducing agent is 0.9% for C30, 1.0% for C40 and 1.1% for C50. The mix proportion design of concrete is shown in Table Concrete block In order to study on the relationship between hardness and strength under the action of sulfate attack, two types of molding specimens, namely group A and group B, are made. The size of group A is 100 mm 100 mm 100 mm, which is used to test the compressive strength. The size of group B is 100 mm 100 mm 400 mm, and it is used to detect the change of dietmar Leeb, dynamic elastic modulus and mass loss. For details of concrete test block see attached in Figure.1 [6]. Fig. 1. Concrete test block 3.3. Concentration of sulfate This experiment takes Na 2 SO 4 as the concentration of sulfate. According to the grade of corrosion environment on water and soil, which is shown in Table 3. The concentration of sulfate is confected in different concentration, from 0 mg/l, 1000 mg/l, 4000 mg/l to 7000 mg/l. It regards 0 mg/l as the basic concentration leavel, and the 1000 mg/l, 4000 mg/l and 7000 mg/l are represented as V-C, V-D and V-E respectively [7].

4 194 SHEN LIN, WANG SHAOPENG, ZHAO SHANGCHUAN, LI WANHENG Table 3. Grade of corrosion environment on water and soil ``` ``` Factor ```` Level Sulfate ion concentration in water (mg/l) Soil sulfate ion concentration water-soluble value (mg/l) V-C V-D V-E Process of experiment The method of wetting and drying on concrete members is reference to the standard of ordinary concrete long-term performance and durability test method [8]. In the experimental process, the specimens are firstly enclosed in a box that filled with concentration of sulfate, then the specimen is dry out for 30 minutes after soaking for 16 hours. After that, the specimens are stetted into the baking chamber at 80 ± 5 C for 6 hours, and cooled for 2 hours after that. Repeat these steps until the number of cycles reached 15, 30, 60, 105, 165, 210 times, then compressive strength is carried out on group A, and the dynamic modulus of elasticity on group B. For details see attached Figure 2. Fig. 2. Baking chamber for specimens 4. The test results analysis 4.1. Relationship between hardness and strength of concrete Concrete strength and hardness values in the test are summarized in Table 4, which give its change rule. The data of test shows that when the repeat tests after 150 times, the strength of concrete specimens shows slowly declined.

5 STUDY ON DURABILITY TESTING OF CONCRETE UNDER THE CONDITION 195 strength grade C30 C40 C50 Table 4. Concrete strength and hardness values of the table concentration 0 mg/l 1000 mg/l 4000 mg/l 7000 mg/l strength hardness strength hardness strength hardness strength hardness Table 5. Strength and hardness values in 5% sodium sulfate C30 C40 C50 strength hardness strength hardness strength hardness In order to study the effect of different concentrations on the strength of concrete after sulfate attack, 5% concentration sulfate attack test is carried out. The test is

6 196 SHEN LIN, WANG SHAOPENG, ZHAO SHANGCHUAN, LI WANHENG the same process of experiment above. According to the result in Table 5, it shows that under the high-concentration sulfate attack, the concrete strength shows a significant decrease. It carry out the fitting analysis based on the acquired data Table 4 and Table 5 to realize the relationship between strength of concrete and hardness under the condition of sulfate, as it shows in Figure 3. Fig. 3. The fit map of Concrete hardness and strength LH = f c (1) Where LH denotes Leeb hardness, f c denotes the concrete compressive strength. By the formula (1), the strength of specimen can be calculated from the hardness in the sulfate attack, which can be used to judge the damage level of the specimen Critical hardness This is clear from the stand for test methods of Long-Term Performance and Durability of ordinary concrete that the standard for terminating of strength is about 0.75 time of compressive strength [9]. According to the principle of 0.75 times strength, the critical hardness of strength 30Mpa, 40Mpa, 50Mpa, 60Mpa, 70Mpa and 80Mpa are proposed, as shown in Table 6. Compareing with the value of hardness and critical hardness from Table 6, the formula of critical hardness is obtained with application of least-square method LH D = 0.75LH w (2) In the formula (2), LH w denotes hardness in the same ages without being sulfate attack, which also can be used for comparison the specimens by core sampling: LH D denotes the critical hardness of concrete under the condition of sulfate. For predicting the durability of sulfate-eroded concrete components, the value of hardness obtained without being sulfate attack is taken as the reference hardness value

7 STUDY ON DURABILITY TESTING OF CONCRETE UNDER THE CONDITION 197 LHw, then put them into the formula (2) to get the critical hardness value LHD [10 13]. Table 6. Sulfate erosion critical state critical hardness value Reduce the front intensity/mpa Reduce the after intensity/ Mpa Reduce the front hardness Critical Hardness The hardness value is decreased by percentage Application of bridge Based on the results, It takes a in practical project to calculate the durability of concrete bridge, which shows as Figure 4 and Figure 5. Fig. 4. Pier concrete wet and dry cycle erosion damage situation Fig. 5. Hardness test of pier The test includes the erosion by sulfate and without being sulfate attack on the pier of No.78 # -1. The test area of erosion is selected within 300mm above the contact surface between pier and soil, Eroded parts is above the base surface of 300mm range. For each test site, an average of 12 test areas is selected., and the average result is shown in Table 7. LHx = LHµ 1.645LHσ, LH s = =

8 198 SHEN LIN, WANG SHAOPENG, ZHAO SHANGCHUAN, LI WANHENG Table # -1 column by the hardness of sulfate erosion site test results No.1 No.2 No.3 No.4 No.5 No.6 µ No.7 No.8 No.9 No.10 No.11 No.12 δ The hardness of the column by sulfate attack site hardness can be shown in Table Table # -1 column by Sulfate erosion site hardness test results No.1 No.2 No.3 No.4 No.5 No.6 µ No.7 No.8 No.9 No.10 No.11 No.12 δ The hardness of column without being sulfate attack is: The critical hardness calculation formula: LH w = = LH D = 0.75LH w = = < , namely LH 1 <LH D, Therefore, it is considered that the member has reached the sulfate erosion durability life. 6. Conclusions (1) The relationship between the hardness and the strength of the eroded concrete is established, and it obtaines the critical hardness values of the concrete; (2) The evaluation indexes and method of durability testing on concrete under the condition of sulfate are established; (3) This method can be used for the long-term testing and evaluation of durability of concrete components under the condition of sulfate. References [1] Xue P. F., Xiang Y. Q.: Corrected diffusion model of chloride in concrete and its engineering application. Journal of zhejiang university (engineering science) 44 (2010), No. 4, [2] Funahashi M.: Predicting corrosion free service life of a concrete structure in a chloride environment. ACI Material Journal 87 (1990), No. 6,

9 STUDY ON DURABILITY TESTING OF CONCRETE UNDER THE CONDITION 199 [3] Prezzi M,. Geyskens P., Monteiro P. J. M.: Reliability approach to service life prediction of concrete exposed to marine environments. ACI Material Journal 93 (1996), No. 6, [4] Mangat P. S., Limbachiya M. C.: Effect of initial curing on chloride diffusion in concrete repair material. Cement Concrete Research 29 (1999), No. 9, [5] JGJ : Specification for mix proportion design of ordinary concrete. China (2011). [6] Tixier R., Mobasher B.: Modeling of damage in cement-based materials subjected to external sulfate attack. I: Formulation. Journal of Materials in Civil Engineering 15 (2003), No. 4, [7] GB/T : Code for durability design of concrete structures. China (2009). [8] GB/T : Ordinary concrete Long-term Performance and Durability Test Method Standard. China (2010). [9] JGJ : Specification for mix proportion design of ordinary concrete. China (2000). [10] Masi M., Colella D., Radaelli G., et al.: Simulation of chloride penetration in cement-based materials. Cement and Concrete Research 27 (1997), No. 10, [11] American Society for Testing and Materials: ASTM C452 Standard test method for potential expansion of Portland-cement mortars exposed to sulfate. USA (2006). [12] American Society for Testing and Materials.: ASTM C1012 Standard test method for length change of hydraulic-cement mortars exposed to a sulfate solution. USA (2004). [13] American Society for Testing and Materials: ASTM E632 Standard test method for developing accelerated tests to aid prediction of the service life of building components and materials. USA (1996). Received November 16, 2017

10 200 SHEN LIN, WANG SHAOPENG, ZHAO SHANGCHUAN, LI WANHENG